| Assay Method Information | |
| | Fluorescence Direct Binding Asaay |
| Description: | Determination of the affinities of compounds to protein containing one or more tryptophan is measurable by monitoring the fluorescence emission in direct mode. The measurements, depending on the protein available amounts, were performed either manually in a cuvette on ISS-PCI photon counting spectrofluorometer or automatically in well plates on a fluorescence plate reader device. Fluorescence titrations were performed at 20° C. in the chosen binding assay buffer by using a defined constant protein concentration against ligand concentration variations. Small aliquots of known ligand concentration solubilized in DMSO were added and the fluorescence, excited at 280 nm, was recorded at 340 nm. The fluorescence intensity was corrected for protein dilution and for the filter effect (Birdsall, B., King, R. W., Wheeler, M. R., Lewis, C. A. Jr, Goode, S. R., Dunlap, R. B. & Roberts, G. C. (1983). Anal. Biochem.132, 353-361). The corrected fluorescence intensity was plotted against the ligand concentration and fitted using a four-parameter sigmoidal function from which the equilibrium dissociation constant Kd was computed using the law of mass action assuming a 1:1 protein ligand complex (Eftink, Methods Enzymol. 1997; 278:221-57). The process includes:Optimization of measurement parameters to minimize protein consumption and to minimize the dilution effect and the DMSO content. Titration measurements of the protein against ligand by at least 12 titration steps to obtain an s-curve fit. Repeat the same titration measurements with the ligand alone to enable correction. Check the stability of the protein once by titration against DMSO alone. Determination of the molar extinction coefficients of the ligand at 280 and 340 nm with help of an UV-spectrophotometer. Use Excel template for the correction of the measured raw data. Use GraphPad Prism software for the quadratic binding fit and the KD evaluation. |
| Affinity data for this assay | |
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